Reflector and a receiver for a solar energy collection system

ABSTRACT

The present invention provides a reflector ( 24 ) for a solar energy collection system ( 20 ). The reflector ( 24 ) is arranged for diverting light received from solar energy collectors ( 22 ). The solar energy collectors ( 22 ) are arranged for focusing the collected light to an elongate focal region of the reflector ( 24 ) wherein, the light is further diverted away.

FIELD OF THE INVENTION

The present invention broadly relates to a reflector and to a receiverfor a solar energy collection system. The present invention relatesparticularly, though not exclusively, to a reflector and to a receiverfor reflecting and absorbing solar energy from an array of solar energycollectors.

BACKGROUND OF THE INVENTION

In many countries the demand for environmentally friendly energy sourcesis increasing. For example, radiation from the sun may be converted intoheat or electricity. A solar energy collection system typically includesan array of solar energy collectors, such as an array of reflectors,which collect the sunlight and direct the collected sunlight to areceiver positioned over the array.

Typically the collected sunlight is focussed onto an absorber in thereceiver and heats the absorber locally to a temperature ofapproximately 350° C. However, it is known that the conversionefficiency of the energy from the collected sunlight to electricity isbetter at higher temperatures such as temperatures of 500° to 600°.Using technology presently available, such high temperatures cause anumber of problems. In order to reach such high temperatures thecollected sunlight needs to be concentrated onto a very small area ofthe absorber. However, especially for large solar collection arrays,radiation from collectors typically reaches the absorber with a verysmall angle of incidence which results in beam broadening andconsequently in loss of concentration. This may be avoided bypositioning the receiver very high over the array of collectors.However, the receiver typically is a heavy and complex device and thepositioning of the absorber at a position that is sufficiently high is achallenge for construction and is expensive.

Further, typical receivers comprise an absorbing body positioned in anevacuated glass housing and typically cannot withstand temperatureshigher than approximately 350° C. Consequently, there is a need for analternative technological solution.

SUMMARY OF THE INVENTION

The present invention provides in a first aspect a reflector for a solarenergy collection system, the reflector being arranged for divertingradiation received from solar energy collectors, the solar energycollectors being arranged for focusing the collected light to anelongate focal region and the reflector comprising at least one elongatereflecting surface portion arranged to divert radiation received from asolar energy collectors.

For example, the reflector may in use be positioned at a level above thesolar energy collectors, which may themselves be primary reflectors, andarranged to divert the radiation in a downward direction to a levelbelow that of the reflector so that the elongate focal region is in useat a level below that of the reflector such as a position on or near aground plane. This has the significant advantage that relatively highangles of incidence of the radiation may be achieved without the need toposition a receiver, which may comprise a further reflector, high abovethe solar energy collectors.

The elongate reflecting surface may be substantially planar, buttypically has a concave or convex cross-sectional shape in a planeperpendicular to the direction of elongation.

The elongate reflecting surface portion may have a cross-sectional shapethat varies in the direction along the elongation. For example, thereflector may also have a first region having a concave cross-sectionalshape and a second region having a convex cross-sectional shape.Typically, however, the reflector has a cross-sectional shape that issubstantially constant in the direction of the elongation of thereflecting surface portion. In one specific embodiment thecross-sectional shape of the elongate reflecting surface portion isconcave. For example, the concave reflecting surface portion maycomprise a plurality of surface portions or segments which may bejoined. In this case, the reflecting surface portion may comprise aplurality of substantially planar reflecting portions which are arrangedin a concave shape. Alternatively the reflecting surface may comprise aconcave layer which may be integrally formed.

The present invention provides in a second aspect a receiver for a solarenergy collection system, the receiver comprising:

a housing having an interior space which can be evacuated and alight-transmissive window for transmission of light through the windowinto the interior space,

an absorbing body positioned in the interior space of the housing forabsorbing the light,

wherein the receiver is arranged for evacuation of the interior spaceusing a vacuum pump during use of the receiver.

The housing of the receiver may be arranged for connection to the vacuumpump. The vacuum pump may be an external pump, but may also be aninternal pump that may be positioned in the housing (for example agetter pump).

The receiver has a number of advantages. Because the interior space canbe evacuated by the vacuum pump during use of the receiver, heatconduction from the absorber body to the window, which may be a glasswindow, is reduced and consequently the window has in use typically atemperature that is much lower than that of the absorber body.Consequently, the receiver is suitable for higher temperatures thanconventional receivers.

Direct contact between the absorber body and the window typically can beavoided. The housing typically comprises a material that is thermallyinsulating and is arranged to reduce heat conduction from the absorbingbody to the window which further increases suitability for hightemperatures. For example, the housing may comprise an inner portionwhich may be metallic and an outer portion which may comprise thethermally insulating material.

Further, supports, such as pilar-type supports, which support theabsorber body in the housing may comprise the thermally insulatingmaterial. The thermally insulating material typically is a ceramicsmaterial.

The absorber body may have any suitable shape but typically is shaped sothat at least a portion of the light that is reflected by a surfaceportion of the absorber body is reflected to another surface portion ofthe absorber body. For example, if the light is reflected three timesand each time 80% of the light is absorbed, only less than 1% of thelight may escape. In a specific embodiment of the present invention theabsorber body has a substantially U-shaped or V-shaped cross-sectionalshape. The substantially U- or V-shaped absorber body has the advantageof having a larger surface to volume ratio than a conventional absorberbody which typically is a pipe having a round cross-sectional shape.Consequently, the substantially U- or V-shape of the absorber bodyincreases the absorption efficiency.

The receiver may be arranged for heating of any suitable material suchas a gas or a liquid. In one embodiment the absorber body comprises aconduit for a fluid that is in use directed through the absorber body.For example, the conduit may also have a substantially V- or U-shapedcross-sectional shape. If the fluid is a liquid that is in use directedthrough the absorber body and heated by the absorber body, this shape ofthe conduit has a particular advantage. Liquids may form bubbles whenheated which would diffuse to areas near end portions of the legs of thesubstantially V- or U-cross-sectional shape of the conduit. However,other regions of the conduit would be largely bubble free and canefficiently absorb heat. If the conduit had a round cross-sectionalshape, bubbles would be located in areas where typically the main amountof heat is received which would be of detriment for the absorptionefficiency.

The absorber body may comprise any suitable material but typicallycomprises an absorptive surface coating such as a highly absorptive“black body” type surface coating. The absorber body may also have asolar selective coating such as a coating that absorbs sunlight but onlyemits a relatively small amount of infrared radiation. The housingtypically has an interior surface portion that is reflective so thatsolar light that is directed to the interior surface is reflected to theabsorber body and heat loss is reduced. For example, the housinginterior surface may comprise a metallic material that is reflective.

The receiver may be arranged for receiving radiation collected by aplurality of collectors which focus the collected light to an elongatedfocal region such as a linear focal region. In this case, the absorberbody typically is elongated so that the absorber body can receive theradiation associated with the elongated focal region.

The present invention provides in a third aspect a solar energycollection system comprising the reflector according to the secondaspect of the present invention.

Because the reflector in use diverts radiation to the receiver, it ispossible to avoid relatively small angles of incidence without the needto position the absorber at a very high level above the solar energycollectors. As relatively small angles of incidence can be avoided, lossof concentration due to broadening of the beam is reduced and it ispossible to achieve higher absorber body temperatures.

The solar energy collection system according to the third aspect of thepresent invention typically comprises a receiver such as the receiveraccording to the first aspect of the invention. The reflector typicallyis positioned at a level above the solar energy collectors and arrangedto divert the radiation in a downward direction. The receiver may bepositioned on a ground plane. An elongate focal region of the solarenergy collection system typically is in use directed into the receiverof the solar energy collection system.

Alternatively, the solar energy collection system may not comprise areceiver but may be arranged for direct heating of a material such as asolid material. For example, the solar energy collection system may bearranged for heating of a solid fuel such as brown coal. Australianbrown coal has a relatively large concentration of moisture which is ofdisadvantage for combustion. The solar energy collection system may bearranged for heating of the brown coal and thereby reducing moistureconcentration in the brown coal.

The reflector may comprise two or more concave reflecting surfaceportions. For example, the reflector may comprise two concave reflectingsurface portions arranged so that the reflector has a cross-section thatcomprises two concave portions. In this case, the system typically isarranged so that the reflector is positioned over the receiver withcollectors positioned on either side of the receiver and respectiveconcave reflecting surface portions divert radiation received from solarenergy collectors located at respective sides of the reflector.

The invention will be more fully understood from the followingdescription of specific embodiments of the invention. The description isprovided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a receiver for a solar energycollection system according to a specific embodiment of the presentinvention,

FIG. 2 shows a cross-sectional view of a solar energy collection systemaccording to a specific embodiment of the present invention,

FIG. 3 shows a top-view of the solar energy collection system shown inFIG. 2, and

FIG. 4 shows a cross-sectional view of a reflector according to anembodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring initially to FIG. 1, a receiver 10 for a solar energycollection system according to a specific embodiment of the presentinvention is now described.

The receiver 10 comprises a housing 12 which has an interior space 13.An absorber body 14 is positioned in the interior space 13 and a window16 closes the interior space. The window 16 is composed of a lighttransmissive material such as glass. The interior space 13 is in useevacuated using vacuum pump 17.

The receiver 10 is arranged to receive solar radiation through thewindow 16 and to absorb the solar radiation by the absorber body 14. Inthis embodiment the absorber body 14 has a shape that increaseslikelihood for multiple reflections of received solar light. In thisexample, the absorber body 14 has a U-shaped cross-sectional shape. Theabsorber body 14 in this example is composed of a metallic materialwhich has a “black body” coating to increase the absorption of receivedsunlight. Due to the likelihood for multiple reflections of the receivedsunlight by the absorber body 14 the absorption efficiency is increased.

In a variation of this embodiment the absorber body 14 is coated with asolar reflective coating, such as a coating that has a relatively highabsorption efficiency for solar light and a relatively low emissionefficiency for infrared radiation. Such a layer may comprise a ceramicmaterial having a graded metal concentration.

Supports 18 support the absorber body 14 in the housing 12. In thisexample the supports 18 are composed of a thermally insulating material,such as a ceramics material. Due to the thermally insulating material,heat conduction from the absorber body 14 through the housing 12 to theglass window 16 is reduced. Consequently, the receiver 10 is suitablefor relatively high temperatures. In this embodiment the housing 12comprises an inner portion that is metallic and an outer portion that isthermally insulating and in this example also is composed of thethermally insulating ceramics material.

It will be appreciated that in variations of this embodiment the housing12 may be composed of any suitable material, such as a metallicmaterial. Further, if the housing 12 comprises a thermally insulatingmaterial, the supports 18 may not necessarily be composed of a thermallyinsulating material.

The absorber body 14 may be arranged for heating a fluid that istransmitted through the absorber body 14. The absorber body 14 typicallycomprises suitable conduits (not shown) for transportation of the fluidor the solid material through the absorber body 14.

The receiver 10 may have any substantially square, rounded orrectangular cross-sectional shape in a section parallel to the window16. In this embodiment, however, the absorber 10 and the absorber body14 have a shape which is elongated in the plane of the window 16 and ina direction perpendicular to the plane of the drawing shown as FIG. 1.The receiver 10 therefore is arranged to receive collected solarradiation from a solar energy collection system having a linearlyextended focal region.

It will be appreciated that in variations of this embodiment theabsorber body 14 may have any suitable shape. For example, the absorberbody 14 may be a pipe that conveys a fluid and that may have anycross-sectional shape, such as a round or rectangular shape.

FIGS. 2 and 3 show a solar energy collection system according to aspecific embodiment of the present invention. The system 20 comprises anarray of solar energy collectors 22 which direct collected sunlight viareflector 24 to receiver 26. For clarity, FIG. 3 does not show thereflector 24. In this embodiment each collector 22 is a reflector andthe reflector 24 has a concave reflecting surface. Because of thereflector 24 it is possible to maintain relatively high angle ofincidence for radiation received by the receiver 26 without the need toposition the absorber high above the solar energy collectors.

In the embodiment shown in FIG. 2 the radiation collected by collectors22 is directed to respective portions of the reflector 24.

For example, the reflecting surface may be a film deposited on a concavesubstrate. Alternatively, the reflector 24 may be composed of areflecting material. Further, the reflector 24 may comprise a pluralityof reflecting surface portions which may be connected. In this case,each of the surface portions may be planar and the plurality of thereflecting portions may be connected so that the reflector 24 has aconcave reflecting surface.

In this embodiment the receiver 26 is positioned on a ground plane. Forexample, the receiver 26 may be the receiver 10 shown in FIG. 1 asdiscussed above. The reflector 24 typically comprises a metallicreflective surface coating but may alternatively comprise any othersuitable reflective coatings or may be composed from a reflectivematerial. In this embodiment the reflector 24 is elongated in adirection perpendicular to the plane of the drawing shown in FIG. 2 andthe receiver 26 has a corresponding elongated shape which is also shownin FIG. 3.

Dashed line 30 is provided in order to illustrate a variation of thisembodiment. The dashed line 30 represents a plane of symmetry for thereflector 24 and the receiver 26. In this case the reflector 24comprises two concave reflecting portions which is further illustratedby the reflector 32 shown in FIG. 4. The solar energy collectors 22 arearranged on either side of the dashed line 30 and respective concaveportions of the reflector 24 divert solar radiation received fromrespective sides of the system. FIG. 4 shows the reflector 32 having twoconcave reflecting portions 34 and 36 and supports 38.

In a further variation of the embodiment shown in FIGS. 2 and 3 thesolar energy collection system may not comprise a receiver, but may bearranged for direct heating of a material, such as a fuel (eg. browncoal).

Although the invention has been described with reference to particularexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms. For example, it will beappreciated that collectors 22 may not necessarily be mirrors but mayalso be lenses, such as a Fresnel lenses. Further, the collectors 22 maynot be arranged in an array. In the embodiments discussed above, thereflector 24 has a concave reflecting surface. It will be appreciatedthat in variations of this embodiment the reflector 24 may also have aconvex reflecting surface. In this case the positions of the collectors22 will be adjusted so that focussing of the collected sunlight onto theabsorber is possible.

In addition, the person skilled in the art will appreciate that thereflector 24 may be replaced by a suitable mirror which may be combinedwith a lens such as a Fresnel lens to have similar optical properties asthe concave or convex reflector 24.

Further, the focal region of the solar energy collection system may notnecessarily be linear but may alternatively have any other shapeincluding partially curved or angled shapes. The receiver may also beshaped to receive sunlight from a solar energy collection system havingany shape for the focal region.

1. A reflector for a solar energy collection system, the reflector beingarranged for diverting radiation received from solar energy collectors,the solar energy collectors together being arranged for focusing thecollected light to an elongate focal region and the reflector comprisingat least one elongate reflecting surface portion arranged to divertradiation received from the solar energy collectors.
 2. The reflector asclaimed in claim 1 wherein the elongate reflecting surface has a concavecross-sectional shape in a plane perpendicular to the direction ofelongation.
 3. The reflector as claimed in claim 1 wherein the elongatereflecting surface has a convex cross-sectional shape in a planeperpendicular to the direction of elongation.
 4. The reflector asclaimed in claim 1 comprising a first region having a concavecross-sectional shape and a second region having a convexcross-sectional shape.
 5. The reflector as claimed in claim 1 whereinthe elongate reflecting surface portion has a cross-sectional shape thatis substantially constant in the direction of the elongation of thereflecting surface portion.
 6. The reflector as claimed in claim 1wherein the reflecting surface portion comprises a plurality of surfaceportions.
 7. The reflector as claimed in claim 1 wherein the reflectingsurface comprises a concave layer.
 8. A receiver for a solar energycollection system, the receiver comprising: a housing having an interiorspace which can be evacuated and a light-transmissive window fortransmission of light through the window into the interior space, anabsorbing body positioned in the interior space of the housing forabsorbing the light, wherein the receiver is arranged for evacuation ofthe interior space using a vacuum pump during use of the receiver. 9.The receiver as claimed in claim 8 being arranged for connection to thevacuum pump.
 10. The receiver as claimed in claim 8 wherein thermallyinsulating material is provided in the form of supports which supportthe absorber body in the housing.
 11. The receiver as claimed in claim 8wherein at least a portion of the housing comprises a thermallyinsulating material.
 12. The receiver as claimed in claim 8 wherein theabsorber body is shaped so that at least a portion of the light that isreflected by a surface portion of the absorber body is reflected toanother surface portion of the absorber body.
 13. The receiver asclaimed in claim 8 wherein the absorber body has a substantiallyU-shaped cross-sectional shape.
 14. The receiver as claimed in claim 8wherein the absorber body has a substantially V-shaped cross-sectionalshape.
 15. The receiver as claimed in claim 8 being arranged for heatingof a fluid.
 16. The receiver as claimed in claim 8 wherein the absorberbody comprises a conduit for a fluid that is in use conducted throughthe absorber body.
 17. The receiver as claimed in claim 16 wherein theconduit has a substantially V-shaped cross-sectional shape.
 18. Thereceiver as claimed in claim 16 wherein the conduit has a substantiallyU-shaped cross-sectional shape.
 19. The receiver as claimed in claim 8being arranged for receiving radiation collected by a plurality ofcollectors which focus the collected light to an elongated focal region.20. A solar energy collection system comprising: solar energycollectors, the solar energy collectors together being arranged forfocusing collected light towards an elongate focal region and thereflector as claimed in claim 1 for diverting collected light to areceiver.
 21. A solar energy collection system as claimed in claim 20wherein the reflector is positioned at a level above the solar energycollectors and arranged to divert the radiation in a downward direction.22. The solar energy collection system as claimed in claim 20 whereinthe receiver comprises: a housing having an interior space which can beevacuated and a light-transmissive window for transmission of lightthrough the window into the interior space, an absorbing body positionedin the interior space of the housing for absorbing the light, whereinthe receiver is arranged for evacuation of the interior space using avacuum pump during use of the receiver.
 23. The solar energy collectionsystem as claimed in claim 22 wherein an elongate focal region of thesolar energy collection system is directed into the receiver.
 24. Thesolar energy collection system as claimed in claim 22 wherein thereceiver is in use positioned below the reflector.
 25. The solar energycollection system as claimed in claim 24 wherein the receiver is in usepositioned on a ground plane.
 26. The solar energy collection system asclaimed in claim 20 wherein the receiver comprises: a housing having aninterior space which can be evacuated and a light-transmissive windowfor transmission of light through the window into the interior space, anabsorbing body positioned in the interior space of the housing forabsorbing the light, wherein the receiver is arranged for evacuation ofthe interior space using a vacuum pump during use of the receiver; andbeing arranged for direct heating of a material.
 27. The solar energycollection system as claimed in claim 20 wherein the receiver comprises:a housing having an interior space which can be evacuated and alight-transmissive window for transmission of light through the windowinto the interior space, an absorbing body positioned in the interiorspace of the housing for absorbing the light, wherein the receiver isarranged for evacuation of the interior space using a vacuum pump duringuse of the receiver; wherein the reflector has a concave cross-sectionalshape in a plane perpendicular to the direction of elongation; andwherein the reflector comprises two or more concave reflecting surfaceportions.
 28. The solar energy collection system as claimed in claim 26wherein the system is arranged so that the reflector is positioned overthe receiver with collectors positioned on either side of the receiverand respective concave reflecting surface portions divert radiationreceived from solar energy collectors located at respective sides of thereflector.